Staphylococcus aureus causes a variety of severe human diseases, including septicemia, pneumonia and endocarditis. Its considerable pathogenic potential results from an extensive virulence factor repertoire. The particularly high incidence of antibiotic resistance among human isolates and the potential use of staphylococcal superantigens as bioweapons further highlight the urgent need for developing effective methods for the prevention and control of this ubiquitous pathogen. Preliminary studies and previous investigations have demonstrated that proteins derived from S. aureus grown under iron-restricted conditions provide cross-protection against challenge by multiple strains of S. aureus. These results led to the hypothesis that one or more proteins present in the S. aureus iron-regulated protein-enriched composition after growth under iron-restriction are effective protective antigens. To test this hypothesis, and work toward the overall goal of developing safe and effective therapies to protect against S. aureus infection, Phase I feasibility studies with three specific aims are proposed: in Aim 1 we propose to separate and identify the immunoreactive proteins derived from S. aureus grown under iron-restricted conditions. During Aim 2, individual proteins will be generated and tested for their ability to stimulate specific antibody and cytokine responses in mice. Finally, in Aim 3, the recombinant proteins will be formulated into vaccines and tested for their ability to protect against S. aureus challenge in murine models of systemic and superficial infection. Taken together, these investigations will aid in determining 1) which of the proteins in the IRPE fraction provide protection against S. aureus challenge, and 2) the type of immune responses elicited by the vaccine components. These proposed Phase I feasibility studies will provide sufficient data for the formulation of rational strategies for developing safe and effective vaccines and immunotherapeutic agents against S. aureus infection.